The present invention relates to a DC current source for supplying DC current to a communication terminal device.
For communicating over the telephone, carrier communication system, etc., it has been heretofore necessary to supply DC current to the communication terminal device. In case such a communication terminal device comprises the electronics, however, the supplied DC current was very disadvantageous to the switching and demodulation operations.
According to a prior art for supplying a direct current to a communication terminal device, such as a telephone terminal, a transformer has been utilized between the telephone terminal and an electronic exchange for preventing the direct current from flowing through the electronic device.
In the DC current supply circuit using such a transformer, it was necessary to provide a larger core of the transformer in order to prevent magnetic saturation due to the DC current flowing through the primary subwindings and the transformer, which would restrict such a ransformer device from being manufactured in a smaller size.